fileno, errno: What does the "no" mean? (Non native English)

Question

I'm a non native English so there are idiomatic terms I don't understand.

What does the "no" really means in the function fileno() or the headererrno.h ?

Does the "no" an abbreviation of "number"?

If yes why?

Answer 1

In the man documentation of fileno() this is not explicit but this is written:

The function fileno() examines the argument stream and returns its integer descriptor.

So with this explanation we should say that "no" means file descriptor.

But in the man description of errno there is an explicit description:

errno - number of last error

So we can deduce that "no" really means "number".

Anyway Wikipedia comes to explicit the explanation of the Numero sign:

The numero sign or numero symbol, № (also represented as Nº, No, No./no. (US English),1 or No/no (UK English); plural Nos./nos. (US English) or Nos/nos (UK English)2), is a typographic abbreviation of the word number(s) indicating ordinal numeration, especially in names and titles.

And if you still had some doubts, there is also the Wikipedia page for errno.h that says:

It defines macros for reporting and retrieving error conditions using the symbol errno (short for "error number").